The removal of phosphorus from effluent streams has taken on increasing importance in one modern world. The effect of phosphorus in waste sewage on the lakes and streams into which such sewage flows has been so serious that its removal has been a mandated requirement by multiple governmental authorities. When certain forms of phosphorus are present in lakes, rivers and streams, there is a significant increase in the growth of unwanted bacteria, algae and vegetation; which in turn acts to severely restrict the use that can be made of such waters, and can act to render such water useless, or, can deteriorate the health of man and his environment.
Many processes have been proposed for the removal of phosphorus from waste streams but most have been found to be either too ineffective, or to be too costly to be cost effective. Presently, the most frequently employed method of phosphorus removal is by precipitants. This process is achieved by the addition of metal oxides such as calcium, magnesium and sodium aluminate or by the addition of metal salts, such as chlorides and sulfates of aluminum and iron to the waste stream. Such chemicals can be added at various stages of the treatment process and have been found effective, but not without significant expense and the creation of additional problems.
The metal oxides typically used in such precipitant systems are strongly alkaline and effect a change in pH to the waste stream which may interfere with other processing functions or steps and often requires further treatment before returning such treated stream to the environment. Regulation of pH frequently requires additional equipment, sophisticated controls, further chemical treatment and additional operator attention. The metal salts also create problems in that they are typically strongly acidic. Dealing with them involves problems comparable to those resulting from the use of metal oxides except that an acid condition must be controlled. Additionally, the use of these chemicals requires accurate proportioning of chemical dosages to influent phosphorus loadings for efficient use of the chemicals. Sophisticated controls and/or continuing operator maintainance is required for efficient operation of such precipitant systems.
The use of the chemical precipitant method adds substantially to the cost of water treatment and increases the amount of sludge that must thereafter be disposed of. The precipitate formed in the use of metal salts is voluminous and does not compact well by the usual means employed. Consequently, the more metal salt used the greater the volume of sludge created. The use of metal oxides typically result in a cation contaminated effluent which remains in solution and can present a removal problem that eventually may be mandated for removal by governmental authority.
A promising, but less frequently employed method of phosphorus treatment comprises what is commonly known as the activated sludge process. In such process, biological growth colonies are typically developed in the waste water stream through treatment in the presence of oxygen. A biologically active sludge is thus formed which is recycled to the influent for biochemical reaction with the organisms in the influent to create bioprecipitation, adsorption, absorption and aqueous oxidation. The active microorganisms are periodically or continuously introduced to the reactor. Though such process appears at first glance to be an inexpensive and highly desirable means of removing phosphorus, the activated sludge process of the prior art have, in practice, been less efficient than desired and have required significant additions of precipitate to assure that a clear, substantially phosphorus free effluent, is attained. The low level of efficiency can be directly attributed to the limited phosphorus uptake by the bacteria in the waste stream being treated. By far, the most expensive element of an activated sludge process occurs when additional precipitating chemicals are required and it is not atypical that an activated sludge system may require the use of 50% or more of the chemical precipitant necessary in a phosphorus precipitation process, to obtain an acceptable phosphorus free effluent level.
One object of the instant invention is to improve the efficiency of the activated sludge process to attain greater phosphorus removal without the use of precipitants. Another object of the invention is to reduce the chemical cost of treating phosphorus containing sewage. A further object is to treat phosphorus containing sewage in such a manner which allows creation of an easily compactable sludge to reduce land fill requirements. These and other objects will be apparent from the following disclosure of the invention.